Exercise stool



FIG. 1 is a top, rear, and left side perspective view of an exercise stool, showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a front elevational view thereof; and,

FIG. 5 is a rear elevational view thereof. 

The ornamental design for an exercise stool, as shown and described. 